All Genetic Epidemiology Branch investigations evaluate the contributions of host susceptibility and environmental exposure in the development of cancer. In family studies, a candidate gene for melanoma on 9p, p16, was identified. Germline mutations were identified in most families linked to 9p. Functional studies of p16 mutations were also conducted. Among families with mutations in p16 which interfered with normal function, a 10-fold increased risk of pancreatic cancer was found. No pancreatic cancer occurred in families without p16 mutations. Novel mutations in BRCA1 were described in 8 families, including a family with male breast cancer which was previously thought to be associated with mutations in BRCA2. Preliminary analyses of phenotype/genotype correlations in Neurofibromatosis 2 families have shown no association with type or locations of mutations and clinical severity of disease. Three families with Ewing's sarcoma, melanoma and brain cancers have been tested for p16 mutations and found to have normal p16.